CS320 Web and Internet Programming JSP Scripting Elements and Page Directives Chengyu Sun California State University, Los Angeles

Java Server Page (JSP) Why? It’s tedious to generate HTML using println() Separate presentation from processing How? Java code embedded in HTML documents

HelloJSP1.jsp Hello JSP 1 A JSP without J or S.

HelloJSP2.jsp JSP Hello World Hello World on.

How Does JSP Work? Look under $CATALINA_HOME/work/Catalina/localh ost/context_name JSPServlet convertcompile ByteCode execute automatically done by server

Some Simple Observations about the JSP/Servlets In package org.apache.jsp _jspService() handles everything replaces service() in HttpServlet What happened to doGet(), doPost(),...?? HTML text  out.write(...)

Pre-defined Variables request, response, out session, application config, pageContext page The same request, response, session etc. that are used in servlets – see the Servlet API documentation for what you can do with them.

JSP Components HTML template text Code elements of Java Scripting elements Directives Beans Expression language Custom tag libraries

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JSP Expressions What’s an expression?? in JSP out.write( expression ) in _jspService()

Example: Add.jsp Add two integer parameters and display the sum

JSP Scriptlets All code goes inside _jspService()

Example: Add.jsp Again Add the code to validate the parameters

Another Scriptlet Example Have a nice day! Have a lousy day!

JSP Declarations All code goes outside _jspService()

Example: RequestCounter.jsp Initialize a counter as a class variable Increment the counter each time the JSP is requested

JSP Scripting Elements JSP Expressions JSP Scriptlets JSP Declarations

Directives Affect the overall structure of the JSP Three type of directives page include taglib

Some Page Directives isELIgnored, errorPage, isErrorPage